1. Field of the Invention
The present invention relates to disk drives. More particularly, the present invention relates to breather filters and to leak testing drives equipped with such breather filters.
2. Description of the Prior Art
The typical hard disk drive includes a head disk assembly (HDA) and a printed circuit board assembly (PCBA) attached to a disk drive base of the HDA. The head disk assembly includes at least one magnetic disk, a spindle motor for rotating the disk, and a head stack assembly (HSA) having an actuator assembly having at least one transducer head, typically several, for reading and writing data from the disk. The printed circuit board assembly includes a servo control system in the form of a disk controller for generating servo control signals. The head stack assembly is controllably positioned in response to the generated servo control signals from the disk controller. In so doing, the attached heads are moved relative to tracks disposed upon the disk.
Commonly assigned U.S. Pat. No. 6,618,222 and (which is incorporated herein by reference in its entirety) discloses a breather filter that is effective to both reduce the effects of airflow generated within the disk drive due to rotation of the disks and to regulate and filter the airflow entering the drive. In particular, the breather filter disclosed therein includes a shroud that reduces turbulent airflow within the drive at and near the outer edge of the disk or disks, which turbulent airflow is believed to at least contribute to the cause of a number of problems. Such problems include, for example, an unwanted resonance response of and force on the actuator assembly, an increase in the percent off track values of the associated head, and disk flutter (vibrations induced on the disk or disks). The breather filter also filters airflow entering the disk drive for undesirable particulates and chemical compounds and regulates the humidity within the drive.
The breather filter described in the above-identified patent fits within the disk drive housing and may be attached to one of the surfaces of the disk drive housing (such as the disk drive cover, for example) by means of adhesive. In particular, the breather filter includes a surface that is configured for attachment to the disk drive cover. This surface of the breather filter is not (and cannot be made to be) perfectly flat. This surface, if examined microscopically, may be seen to have a certain roughness, which may be quantified as local differences in elevation (e.g., peaks and valleys) relative to a reference plane. In turn, the surface of the disk drive cover to which the breather filter is to be attached is not perfectly flat either. Indeed, this surface of the disk drive cover also has a certain roughness which, under sufficient magnification, may also be quantified as local differences in elevation relative to a reference plane.
When attaching the breather filter to the surface of the disk drive cover with adhesive, what is attempted is to adhesively mate two uneven surfaces. When the breather filter is attached to the surface of the disk drive cover, the breather filter is pressed against the disk drive cover, with a layer of adhesive between the two elements. Initially, therefore, the layer of adhesive between the disk drive cover and the breather filter is in compression. Afterwards, when the force applied to the elements is removed, the adhesive layer is in tension, causing a force on adhesive layer that tends to separate the breather filter from the disk drive housing cover. The roughness of the breather filter and that of the disk drive cover only exacerbate this tendency of the breather filter to separate from the disk drive cover because the adhesive cannot make good contact with the rough and uneven surfaces. Increasing the thickness of the adhesive layer does not solve this problem. This tendency to separate may reveal itself as an improper seal between the breather filter and the disk drive housing cover. In turn, such an improper seal reduces the effectiveness of the breather filter's ability to control humidity and filter particulates, with consequent undesirable effects upon the operation and reliability of the drive. Co-pending and commonly assigned U.S. patent application Ser. No. 10/877,740 filed on Jun. 25, 2004 addresses this issue by providing, according to one embodiment thereof, a leveling layer formed of a closed cell foam material sandwiched between two layers of adhesive. The free surface of one of the adhesive layers adheres to the drive housing and the free surface of the other adhesive layer adheres to the breather filter. This structure compensates for the uneven surface roughness of the surfaces of the breather filter and of the drive housing and improves the quality of the seal between the breather filter and the drive housing.
Such an improved seal between the breather filter and the disk drive housing does not, however, obviate the need for drive level leak testing of this interface. Current methods for measuring leaks between the breather filter and the housing tend to compromise the seal and create rework and scrap, for the reasons detailed hereunder. Canister-type breather filters have a single inlet air path. Current methods for measuring airflow leaks at the interface between the breather filter and the housing include sealing off this inlet air path with an airtight external pad. The pad is pressed against the filter to render the breather filter air tight. With the breather filter sealed, a leak tester can pressurize the assembly and test the interface for leaks. One of the disadvantages of this method is that the placement of the external pad exerts a force on the breather filter, which may change the seal characteristics of the breather filter-drive housing interface, rendering an accurate measurement of leaks difficult.
Pouch filters are another type of breather filters. Pouch-type breather filters also have a single inlet for air entering the drive. Current methods for testing such pouch-type breather filters usually call for placing a non-functional dummy pouch-type breather filter on the drive housing, in place of the functional pouch-type breather filter. Such dummy breather filters are similar to their fully functional counterparts, except that they do not include any inlet air path. After such a dummy breather filter is installed on the drive housing, the air inlet may be pressurized and the air-tightness of the interface tested. The drawback to this approach is that the dummy breather filter is not a real component and the filter/housing assembly must be re-worked and the dummy filter scrapped, further increasing the manufacturing costs. Further adding to the costs of such testing is the cost of keeping track of such non-functional components and of insuring that such components do not enter the production line.
From the foregoing, it is apparent that improved disk drives that do not require the use of such non-functional components or such destructive leak testing methods are needed. Such improved disk drives should be configured such that the integrity of the seal between breather filter and the disk drive housing may be accurately tested in a non-destructive fashion.